Elucidating CO2 Chemisorption in Diamine-Appended Metal–Organic Frameworks

Abstract

The widespread deployment of carbon capture and sequestration as a climate change mitigation strategy could be facilitated by the development of more energy-efficient adsorbents. Diamine-appended metal–organic frameworks of the type diamine–M2(dobpdc) (M = Mg, Mn, Fe, Co, Ni, Zn; dobpdc4− = 4,4′-dioxidobiphenyl-3,3′-dicarboxylate) have shown promise for carbon capture applications, although questions remain regarding the molecular mechanisms of CO2 uptake in these materials. Here, we leverage the crystallinity and tunability of this class of frameworks to perform a comprehensive study of CO2 chemisorption. Using multinuclear nuclear magnetic resonance (NMR) spectroscopy experiments and van der Waals-corrected density functional theory (DFT) calculations for thirteen diamine–M2(dobpdc) variants, we demonstrate that the canonical CO2 chemisorption products—ammonium carbamate chains and carbamic acid pairs—can be readily distinguished, and that ammonium carbamate chain formation dominates for diamine–Mg2(dobpdc) materials. In addition, we elucidate a new chemisorption mechanism in the material dmpn Mg2(dobpdc) (dmpn = 2,2-dimethyl-1,3-diaminopropane), which involves formation of a 1:1 mixture of ammonium carbamate and carbamic acid and accounts for the unusual adsorption properties of this material. Finally, we show that the presence of water plays an important role in directing the mechanisms for CO2 uptake in diamine–M2(dobpdc) materials. Overall, our combined NMR and DFT approach enables a thorough depiction and understanding of CO2 adsorption within diamine–M2(dobpdc) compounds, which may aid similar studies in other amine-functionalized adsorbents in the future.

Revealing Molecular Mechanisms in Hierarchical Nanoporous Carbon via Nuclear Magnetic Resonance

“…A similar peak at 124.7 ppm was observed in MOF-274. 44 The − 6 ppm chemical shift vis-à-vis free gas-phase CO 2 (127.7 ppm at 1 bar) is due to aromatic ring currents. 51 Therefore, our HNC has excellent CO 2 capacity that, combined with the inexpensive, sustainable, facile, and up-scalable synthesis method, warrants further study with potential application toward carbon-capture technologies.…”

“…43 The adsorption isotherms of acetone/toluene/n-hexane for our HNC were acquired by using a sorption analyzer at 298 K with N 2 as the carrier gas, as shown in Figure 3C. The proton ( 1 H) single-pulse NMR spectra of liquid acetone, toluene, and n-hexane spectra adsorbed at various loadings were deconvoluted and integrated using dmfit software ( ), 44 thus providing the amount (in mmol) of adsorbed in-pore VOC per gram of HNC (Figure 3C). For comparison of NMR uptake with gas-sorption studies, the abscissa is given as mmol of VOC adsorbed.…”

“…The rotor containing samples was then put into a home-built gas setup (Figure 6B). 44 Before dosing with 13 CO 2 gas (Sigma-Aldrich, 99 atom % 13 C, <3 atom % 18 O), the samples were evacuated for 10 min. 13 CO 2 dosing was carried out overnight to reach equilibration at room temperature (~298 K).…”

Shaping and silane coating of a diamine-grafted metal-organic framework for improved CO2 capture

“…Moreover, a new peak appeared at 163 ppm, which is attributed to the carbamate carbon generated after CO 2 adsorption (for solid-state 13 C NMR spectra see Supplementary Fig. 30) 45 . Meanwhile, the peaks related to the carbons of the silane were mostly unchanged, suggesting that the silane does not affect the CO 2 adsorption mechanism.…”

Stepped enhancement of CO2 adsorption and separation in IL‐ZIF‐IL composites with shell‐interlayer‐core structure

“…Outer shell, interlayer, as well as inner core work as the “micro‐tray” to separate gas mixtures. The nanoparticles of this composite can be considered as a “micro‐rectifying tower,” and a large number of them form an array of “micro‐separation unit.” CO 2 capture was selected to be the target, which has attracted increasing research attentions during the past decade because of the world‐wide concerns about global warming and climate change 13‐22 . Thanks to the feature of such shell‐interlayer‐core structure combining the chemical properties of ZIF‐8 and ILs, the separation performance of CO 2 can be gradually enhanced with high selectivities, for example, 260–1,990 for CO 2 /CH 4 (50:50) and 1,688–5,572 for CO 2 /N 2 (15:85) mixtures using ideal adsorbed solution theory (IAST) predictions.…”